Waterless cleaning system and method for solar trackers using an autonomous robot

ABSTRACT

A solar tracker waterless cleaning system for cleaning solar panels of a solar tracker being able to be positioned at a pre-determined angle, including a docking station and an autonomous robotic cleaner (ARC), the docking station coupled with an edge of the solar tracker, the ARC including at least one rechargeable power source, at least one cleaning cylinder and a controller, the cleaning cylinder including a plurality of fins which rotates for generating a directional air flow for pushing dirt off of the surface of the solar tracker without water, the controller including a motion sensor for determining an angle of the solar tracker and a heading of the ARC, the docking station including at least one electrical connector for recharging the rechargeable power source, the controller for controlling a cleaning process of the ARC and for transmitting and receiving signals to and from the ARC.

CROSS-REFERENCE TO RELATED APPLICATIONS

This international patent application claims priority to and the benefitof each of the following two provisional US patent applications and alsoeach of the following two non-provisional US patent applications:provisional U.S. patent application Ser. No. 62/450,584 filed on Jan.26, 2017; provisional U.S. patent application Ser. No. 62/470,342 filedon Mar. 13, 2017; non-provisional U.S. patent application Ser. No.15/727,055 filed on Oct. 6, 2017; and non-provisional U.S. patentapplication Ser. No. 15/826,976 filed on Nov. 30, 2017. Each of thesefour US patent applications is incorporated in its entirety into thisinternational patent application.

FIELD OF THE DISCLOSED TECHNIQUE

The disclosed technique relates to the cleaning of solar trackers, ingeneral, and to methods and systems for cleaning solar trackers withoutwater using an autonomous robot, also under various wind conditions, inparticular.

BACKGROUND OF THE DISCLOSED TECHNIQUE

The challenges of global climate change and energy circuitry demandshave made the development of renewable energy alternatives vital for thefuture of mankind. The use of direct sun radiation on solar panels canpotentially produce more than enough energy to meet the energy needs ofthe entire planet. As the price of solar power decreases and thepollution caused by conventional fuels is rising, the solar business hasentered a new era of worldwide growth.

In order to bring technologies to exploit solar energy one step closerup to par with conventional fuels, the efficiency rate of solar systemsmust improve. Solar panel efficiency depends amongst other things on thecleanliness of their surface. Energy losses caused by dust and soilingcan reach over 40%. In desert areas, where many solar parks are located,the soiling and dust problem is significant.

A fast growing type of solar park is the solar tracker park. The solartrackers have the ability to follow the sun's position continuously frommorning to evening by changing their tilt angle from east (in themorning) to west (in the evening) in order to increase efficiency.Automatic cleaning solutions for solar trackers usually involve highvolumes of water and/or the installation of special grids in the solartracker park for moving automatic cleaners from solar tracker to solartracker. Such solutions are not cost effective and require added laborfor installation.

Systems for cleaning solar panels are known in the art. US patentapplication publication no. 2015/0272413 A1 to Miyake et al., entitled“Autonomous-Travel Cleaning Robot” is directed to a self-propelledcleaning robot that can efficiently clean a flat surface even if a stepis formed. The cleaning robot can self-travel on a structure to clean aflat surface of the structure, the structure being installed in anoutdoor location. The robot includes a robot main body in which aself-propelled moving means is provided, a cleaning unit that isprovided in a front portion and/or a rear portion of the robot mainbody, and a controller that controls activation of the moving means. Thecontroller includes an attitude controller that detects an attitude ofthe robot main body. The attitude controller includes a floatingdetection sensor that detects floating in one of the front portion andthe rear portion of the robot main body. The controller controls theactivation of the moving means such that the cleaning unit passesthrough a place where the floating is detected after the floating iseliminated. Similar structures are disclosed in US patent applicationpublication nos. 2015/0236640 A1 and 2015/0229265 A1.

Many state of the art solar trackers are covered with an anti-reflectivecoating for increasing solar energy production efficiency. The use ofrobotic cleaners travelling over such solar trackers can ruin anddestroy the anti-reflective coating within a few months. This is due tothe weight of the robotic cleaner travelling over the surface of thesolar panels and to the force at which cleaning brushes on the roboticcleaner impact and press on the surface of the solar panels as thebrushes clean the surface. Solar tracker park owners can thus increasesolar energy production efficiency by reapplying the anti-reflectivecoating, thus increasing the costs of maintaining the solar trackerpark, or by not using an anti-reflective coating, thus not maximizingsolar energy production.

Solar trackers are used the world over and are located in locationswhich can have varying wind conditions. A concern for solar tracker parkowners using a cleaning robot is the safety and durability of thecleaning robot under varying wind conditions. A heavier robotic cleaner,as mentioned above, may prevent the robotic cleaner from being liftedoff the surface of a solar tracker under heavy wind conditions howeverthe increased weight may ruin and destroy the anti-reflective coatingused to increase solar energy production efficiency. There is thus aneed for systems and methods for cleaning solar trackers using acleaning robot wherein the weight of the robot will not ruin anyanti-reflective coating on the solar trackers and wherein the safety ofthe cleaning robot is not compromised even under heavy wind conditions.

SUMMARY OF THE DISCLOSED TECHNIQUE

It is an object of the disclosed technique to provide a novel method andsystem for a solar tracker waterless cleaning system for cleaning solarpanels of a solar tracker. The solar tracker is able to be positioned ata pre-determined angle. The solar tracker waterless cleaning systemincludes a docking station and an autonomous robotic cleaner (ARC). Thedocking station is coupled with an edge of the solar tracker. The ARCincludes at least one rechargeable power source, at least one cleaningcylinder and a controller. The cleaning cylinder is for cleaning dirtoff of a surface of the solar tracker without water and the controlleris for controlling a cleaning process of the ARC and for transmittingand receiving signals to and from the ARC. The controller includes amotion sensor. The cleaning cylinder further includes a plurality offins. The motion sensor is for determining an angle of the solar trackerand a heading of the ARC and the fins rotate for generating adirectional air flow for pushing dirt off of the surface of the solartracker. The docking station includes at least one electrical connectorfor recharging the rechargeable power source. The ARC can anchor in thedocking station and the ARC cleans the solar tracker when the solartracker is positioned at the pre-determined angle. The pre-determinedangle is between −10 to +10 degrees from a horizontal angle of zerodegrees. The motion sensor is used for navigating the ARC over thesurface of the solar tracker. The fins touches the surface of the solartracker when they rotate and the ARC cleans the solar tracker by thedirectional air flow and the touch of the fins pushing dirt off of thesurface of the solar tracker.

In accordance with another aspect of the disclosed technique, there isthus provided a method for waterlessly cleaning a solar trackerincluding at least one autonomous robotic cleaner (ARC) which cleanswithout water. The ARC includes a motion sensor for navigation and thesolar tracker is able to be positioned at a pre-determined angle. Themethod includes the procedures of positioning the solar tracker at thepre-determined angle during nighttime hours, calibrating the motionsensor to a local north of the solar tracker, providing a start cleansignal to the ARC to clean a surface of the solar tracker and cleaningthe solar tracker by using a directional air flow to push dirt off ofthe surface of the solar tracker. The pre-determined angle is between−10 to +10 degrees from a horizontal angle of zero degrees and the ARCnavigates over the surface of the solar tracker using the motion sensor.

In accordance with a further aspect of the disclosed technique, there isthus provided a fixed angle solar table waterless cleaning system forcleaning solar panels of a solar table. The solar table is fixed at apre-determined angle. The solar table waterless cleaning system includesa docking station and an autonomous robotic cleaner (ARC). The dockingstation is coupled with an edge of the solar table. The ARC includes atleast one rechargeable power source, at least one cleaning cylinder anda controller. The cleaning cylinder is for cleaning dirt off of asurface of the solar table without water and the controller is forcontrolling a cleaning process of the ARC and for transmitting andreceiving signals to and from the ARC. The controller includes a motionsensor for determining a heading of the ARC and the cleaning cylinderfurther includes a plurality of fins which rotates for generating adirectional air flow for pushing dirt off of the surface of the solartable. The docking station includes at least one electrical connectorfor recharging the rechargeable power source. The ARC can anchor in thedocking station. The pre-determined angle is between −10 to +10 degreesfrom a horizontal angle of zero degrees. The motion sensor is used fornavigating the ARC over the surface of the solar table. The fins touchthe surface of the solar table when they rotate and the ARC cleans thesolar table by the directional air flow and the touch of the finspushing dirt off of the surface of the solar table.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed technique will be understood and appreciated more fullyfrom the following detailed description taken in conjunction with thedrawings in which:

FIG. 1 is a side view of a plurality of solar trackers in a solartracker park, constructed and operative in accordance with an embodimentof the disclosed technique;

FIG. 2 is a side view of a solar tracker at various times of the 20 day,constructed and operative in accordance with another embodiment of thedisclosed technique;

FIG. 3 is a top view of two neighboring solar trackers including roboticcleaners, constructed and operative in accordance with a furtherembodiment of the disclosed technique;

FIG. 4 is a detailed top see-through view of a first robotic cleaner anda first docking station, constructed and operative in accordance withanother embodiment of the disclosed technique;

FIG. 5 is a cross-sectional view of the robotic cleaner of FIG. 4 alonga line A-A, constructed and operative in accordance with a furtherembodiment of the disclosed technique;

FIG. 6 is a top view of a second docking station, constructed andoperative in accordance with another embodiment of the disclosedtechnique;

FIG. 7 is a side view of the second docking station of FIG. 6, along aline C-C of FIG. 6, constructed and operative in accordance with afurther embodiment of the disclosed technique;

FIG. 8 is another side view of the second docking station of FIG. 6,along a line D-D of FIG. 7, constructed and operative in accordance withanother embodiment of the disclosed technique;

FIG. 9 is a side view of a solar tracker, positioned to enable cleaningby a robotic cleaner under strong wind conditions, constructed andoperative in accordance with a further embodiment of the disclosedtechnique;

FIG. 10 is a top view of a solar tracker, showing a docking station aswell as cleaning patterns for use in varying wind conditions,constructed and operative in accordance with another embodiment of thedisclosed technique;

FIG. 11 is a magnified top view of the docking station of FIG. 10,constructed and operative in accordance with a further embodiment of thedisclosed technique; and

FIG. 12 is a side view of the docking station of FIG. 10, constructedand operative in accordance with another embodiment of the disclosedtechnique.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The disclosed technique overcomes the disadvantages of the prior art byproviding a solar tracker cleaning system and method without using watervia the use of autonomous robotic cleaners (herein abbreviated ARC)which are lightweight and exert very low pressure on the surface of thesolar panels of the solar tracker, thereby preserving anyanti-reflective coating used on the surface of the solar panels. Eachsolar tracker (also referred to as a solar tracker table) in a solartracker park is equipped with a docking station and an ARC that canclean the surface of a solar tracker autonomously. The robotic cleanercan return to the docking station by itself. The disclosed techniqueprovides for a novel navigation system for the ARC using a 6-axis motionsensor, including an accelerometer and an electronic gyroscope, which iscalibrated to a local north of the solar tracker at the beginning ofeach cleaning cycle. In addition, the docking station includes a lockingmechanism which prevents the ARC from being lifted off the surface ofthe solar tracker and falling off the solar tracker regardless of winddirection, even under extreme wind conditions.

A solar tracker park includes a plurality of solar tracker tables. Eachsolar tracker table is constructed from a frame that can change its tiltangle from eastward in the morning to westward in the evening. The solartracker tables are positioned horizontally in a north-south direction.Each frame includes a plurality of solar panels as well as anelectromechanical mechanism for changing the tilt angle of the solartracker table.

The tilt angle of the solar tracker tables is centrally controlled. Thesystem and the method of the disclosed technique includes a plurality ofARCs, with each solar tracker table have its own individual ARC and adedicated docking station. Each ARC is equipped with a rechargeablepower source. When it is not in the process of cleaning a solar trackertable, the ARC is docked in the docking station where the rechargeablepower source can be recharged, thus not interrupting the electricityproduction of the solar tracker table while also recharging itself. Thedocking station may be located on the northern or southern side of thesolar tracker table (northern side for the northern hemisphere, southernside for the southern hemisphere), in order to avoid casting a shadow onthe solar panels during daylight hours. The docking station also enablesthe ARCs to anchor themselves during periods of inclement weather thusavoiding the issue of ARCs falling off the solar tracker tables in badweather or possibly damaging the solar panels of the solar tracker. Thetilt angle of the solar trackers can be controlled to compensate forstrong winds thus enabling the ARC to clean the surface of a solartracker even under strong wind conditions. In addition, according to thedisclosed technique, a novel cleaning pattern can be used by an ARC tomove dust, dirt and debris off the surface of a solar tracker in thepresence of wind conditions, thereby using the wind to increase theefficiency of the cleaning of the surface. According to the disclosedtechnique, the central controller of the solar tracker tables mayinclude a weather center including instruments for measuring wind speed(anemometer), pressure (barometer), humidity (hygrometer) and otherindicators of the weather. The central controller may also be coupledwith a weather information center via a network. The central controllercan aggregate weather information along with the tilt angle of the solartracker tables over various periods of time to improve predictivemaintenance of the solar tracker tables and also to enable machinelearning of the maintenance cycle of the solar tracker tables.

According to the system and the method of the disclosed technique, inthe nighttime hours (i.e., no sun) when no electricity is beingproduced, the solar tracker tables of the solar tracker park arebrought, via the centrally controlled electromechanical mechanism, to ahorizontal position, wherein the tilt angle (i.e., the east-west angle)is substantially zero. Cleaning the solar tracker tables whilst they aresubstantially horizontal (i.e., within a few degrees of zero degrees,for example ±10 degrees from the horizontal) simplifies the cleaningprocess as well as making the ARCs cost effective since the ARCs do notneed strong motors and braking systems for ascending or descending aninclined solar tracker table. The ARCs can be modeled after floorcleaning autonomous robots, however unlike such autonomous robots theARC of the disclosed technique does not require a bin, dust container orfilter and can simply push dirt and debris off the surface of a solartracker table. Once the solar tracker tables are horizontal, the ARC ofeach solar tracker table drives out of its docking station and cleansthe horizontal surface of the solar tracker table. The ARC may move overthe horizontal surface of the solar tracker table in a zigzag path, ascanning path, a sweeping path or other paths for cleaning the surfaceof the solar tracker table. The specific pattern the ARC uses forcleaning the surface of the solar tracker table may be determined basedupon the current weather and wind patterns as determined by a weathercenter coupled with the solar trackers. The ARC is equipped with atleast one edge sensor for preventing it from falling from the solartracker table. Such edge sensors can be used to navigate the ARC alongthe edges of the solar tracker table. Virtual magnetic walls may also beadded to the solar tracker tables as well as the installation of a lowphysical barrier to the edges of the solar tracker tables as additionalmeasures for preventing the ARC from falling off the solar trackertables. Many solar tracker tables have two sections. According to thedisclosed technique, the two sections are coupled together via a bridge,such that once the ARC of a solar tracker table finishes cleaning afirst section, it can then cross over the bridge to the second sectionand clean it as well. Once the second section is cleaned, the ARC cancross the bridge again and return to the docking station where it cananchor itself to a charging assembly. The charging assembly keeps theARC firmly supported while not in use while also enabling it to couplewith charging elements and to charge its rechargeable power source, suchas a rechargeable battery. A locking mechanism is also provided therebypreventing the ARC from being lifted off the surface of the dockingstation and possibly falling off the solar tracker surface.

Furthermore, according to the disclosed technique, the ARC is equippedwith a cleaning cylinder and fins which create a directional air flowfor removing dirt, dust and debris from the surface of the solartracker. The cleaning cylinder and fins are positioned on the ARC suchthat they make minimal contact with the solar panels, exerting apressure on the surface of the solar panels of less than 0.1 grams percentimeter squared (g/cm²), thus preserving the anti-reflective coatingon the solar panels.

Reference is now made to FIG. 1 which is a side view of a plurality ofsolar trackers in a solar tracker park, generally referenced 100,constructed and operative in accordance with an embodiment of thedisclosed technique. Shown in FIG. 1 are solar trackers 102, supportingpoles 104 for the solar trackers, mechanical arms 106 that control thetilt angle of each solar tracker and a mechanical bar 108 that connectsmechanical arms 106 of a number of solar trackers to anelectromechanical controller 110. Electromechanical controller 110includes a mechanical arm 114 which controls the tilt angle of the solartrackers via the movement of mechanical bar 108 and mechanical arms 106.Ground level 112 of the installation of the solar trackers is shown aswell. Cardinal directions east (E) and west (W) are also shown.

Reference is now made to FIG. 2 which is a side view of a solar trackerat various times of the day, generally referenced 130, constructed andoperative in accordance with another embodiment of the disclosedtechnique. From top to bottom in FIG. 2, a solar tracker is shown in themorning hours as the sun rises from the east, at high noon where thesolar tracker is substantially in a flat position and in the afternoonhours as the sun sets in the west. Identical reference numbers to FIG. 1are used in FIG. 2.

As shown, a solar tracker park includes a plurality of solar trackers.Each solar tracker may be a large single solar panel or a plurality ofsolar panels placed adjacent to one another. Each solar tracker isconstructed from a construction frame that can change its tilt anglefrom eastward in the morning to westward in the evening, as shown inFIG. 2. In a solar tracker park, the solar trackers are positionedhorizontally in a north to south direction. The plurality of solarpanels is attached to the construction frame. And as shown in FIG. 1, anelectromechanical mechanism, such as via mechanical bar 108, is used tochange the tilt angle of the solar tracker.

Reference is now made to FIG. 3 which is a top view of two neighboringsolar trackers including robotic cleaners, generally referenced 150,constructed and operative in accordance with a further embodiment of thedisclosed technique. As shown are two solar tracker tables 152A and152B. Solar tracker tables 152A and 152B are substantially similar tosolar trackers 102 (FIG. 1) and are positioned in a north-southdirection (as shown) such that they can tilt from east to west (alsoshown) during the course of a day. Many solar tracker tables include twosections, such as shown in FIG. 3. Each of solar tracker tables 152A and152B are made up of a plurality of solar panels 154. Plurality of solarpanels 154 may be covered with an anti-reflective coating (not shown)for increasing solar energy production efficiency. According to thedisclosed technique, the two sections of each solar tracker are coupledtogether via a bridge 158. Bridge 158 may be equipped with a solar panel162 for generating electricity for charging the rechargeable powersource of the ARC of the disclosed technique, as explained below. Solarpanel 162 is different than plurality of solar panels 154 which make upeach solar tracker table as the electricity generated from plurality ofsolar panels 154 is used by the solar tracker park to store electricitythat can be sold to clients where the electricity generated from solarpanel 162 is used to recharge and power the ARC of the disclosedtechnique. In addition, one of the sections of solar tracker tables 152Aand 152B may be equipped with a docking station 160. Docking station 160may be located on the northern side or the southern side of the solartracker table depending on which hemisphere the solar tracker table ofthe disclosed technique is installed in. Docking station 160 includes aplurality of anchoring elements 164 and a charging assembly (not shownin FIG. 3) for housing an ARC 166, which is merely shown schematicallyin FIG. 3. Details of ARC 166 are provided below in FIGS. 4 and 5.Plurality of anchoring elements 164 enable ARC 166 to be anchored todocking station 160 during periods of inclement weather. Plurality ofanchoring elements 164 may form part of the charging assembly (notshown) such that ARC 166 can be anchored and recharged simultaneously.Details of docking station 160 are shown below in FIG. 4. Details ofanother embodiment of docking station 160 are shown below in FIG. 6-8.As an autonomous robot, ARC 166 can move in a variety of patterns andpaths over the surface of a solar tracker, for example in a zigzag path(not shown), for cleaning the entire surface of solar trackers 152A and152B.

It is noted that when solar tracker tables 152A and 152B are installed,they are preferably positioned in a north-south direction however theactual direction of solar tracker tables 152A and 152B is dependent onthe instruments and calibration used when installed. For example, solartracker tables 152A and 152B may be installed with docking station 160facing magnetic north, true north or a deviation from one of thosedirections, depending on the instruments used during the solar trackerinstallation and how they were calibrated (or miscalibrated). Asdescribed below, according to the disclosed technique, regardless of theactual direction a solar tracker is positioned, the ARC of the disclosedtechnique calibrates itself to a local north of the solar tracker tableitself, thereby increasing the navigation accuracy of the ARC.

Reference is now made to FIG. 4 which is a detailed top see-through viewof a first robotic cleaner and a first docking station, generallyreferenced 200, constructed and operative in accordance with anotherembodiment of the disclosed technique. FIG. 4 shows a first dockingstation 202 and an ARC 204, which are substantially similar to dockingstation 160 and ARC 166 (FIG. 3) respectively yet shown in greaterdetail. ARC 204 may have a plastic body or may be made from othermaterials (not shown). ARC 204 includes a left drive wheel 206A, a rightdrive wheel 206B, a left direct current (herein abbreviated DC) drivemotor 208A and a right DC drive motor 208B. Left drive wheel 206Aincludes a left wheel encoder 248A and right drive wheel 206B includes aright wheel encoder 248B. A left drive belt 210A couples left drivewheel 206A to left DC drive motor 208A such that left DC drive motor208A can drive left drive wheel 206A. A right drive belt 210B couplesright drive wheel 206B to right DC drive motor 208B such that right DCdrive motor 208B can drive right drive wheel 206B. Left wheel and rightwheel encoders 248A and 248B can be embodied as proximity sensors andcan read the revolutions of each of left drive wheel 206A and rightdrive wheel 206B respectively. For example, left wheel and right wheelencoders 248A and 248B can count the number of links or ribs in eitherthe drive wheels or the drive belts. In one example, the drive wheelsmay have 6 pulses per revolutions, 12 pulses per revolution, or anyother number of pulses per revolution, where each pulse can be countedand read by left wheel and right wheel encoders 248A and 248B. Thus leftwheel and right wheel encoders 248A and 248B can be used to determinethe angular positions of left drive wheel 206A and right drive wheel206B. Together with a control unit 220 (explained below), the wheelencoders enable the control of the turning as well as the linear motionof ARC 204 over the surface of a solar tracker. ARC 204 further includesa cleaning cylinder 212. A plurality of fins, for example a plurality ofmicrofiber fins 214 are coupled with cleaning cylinder 212 for cleaningthe surface of a solar tracker table. Plurality of microfiber fins 214are used for pushing dirt off the surface of a solar tracker table bycreating a directional air flow or stream over the surface of the solarpanels of the solar tracker table. The direction air flow enables thepressure plurality of microfiber fins 214 exerts on the surface of thesolar panels to be less than 0.1 g/cm², which should not damage theanti-reflective coating on the surface of the solar panels. As notedabove, according to the disclosed technique, ARC 204 does not includenor does it require a vacuum bin for collecting debris and dirt or afilter. ARC 204 also includes a cleaning cylinder DC drive motor 216 anda cleaning cylinder drive belt 218 for coupling cleaning cylinder DCdrive motor 216 with cleaning cylinder 212 for driving it. ARC 208further includes a control unit 220 (which can also be referred tosimply as a controller). Control unit 220 includes an at least 6-axismotion sensor 246, a swivel wheel 226 and a rechargeable power source228. At least 6-axis motion sensor 246 includes an electronic gyroscope222 and an accelerometer 224. At least 6-axis motion sensor 246 can alsobe embodied as a 9-axis sensor with the functioning of the magnetometernot being used. At least 6-axis motion sensor 246 can embodied as amotion sensor detecting more than six axes of movement. It is noted thatswivel wheel 226 can be replaced with any supporting structure such as abrush, a piece of plastic, a piece of rubber and the like, forsupporting the rear end of ARC 204. The supporting structure does notneed to move or have moveable parts but should be smooth enough so asnot to cause any damage to the surface of the solar tracker table as theARC moves over its surface. Control unit 220 may also include aprocessor (not shown) and a wireless transmitter-receiver (not shown).Control unit 220 controls the operation of ARC 204, including receivingcommands and transmitting information from the ARC (for example via thewireless transmitter-receiver) to a central controller (not shown).Accelerometer 224 can identify the tilt position as well as the movementof ARC 204. Electronic gyroscope 222 can identify the heading of ARC 204while it is stationary or while it is moving. At least 6-axis motionsensor 246 is used by control unit 220 for navigating ARC 204 over thesurface of a solar tracker table. It is noted that at least 6-axismotion sensor 246 can also be embodied as a 9-axis motion sensor,including a magnetometer (not shown) as well. At least 6-axis motionsensor 246 can be embodied using any known motion sensor that combinesat least an accelerometer with an electronic gyroscope, for example theBNO080 9-axis SiP from Hillcrest Labs™ and other similar motion sensors.Swivel wheel 226 supports the rear portion of ARC 204 while allowing itfull maneuverability. As mentioned above, swivel wheel 226 can beembodied as a support structure that does not involve a wheel and may besimply a piece of rubber or plastic. Rechargeable power source 228 maybe a rechargeable battery, such as a 12 volt Ni-MH (nickel-metalhydride) battery but can also be embodied as other types of rechargeablebatteries such as lead acid, lithium ion, LiFePO4, NiCad and the like.ARC 204 further includes a plurality of recharge connectors 232, asexplained below.

In addition, ARC 204 includes at least one edge sensor, such as aproximity sensor, for identifying and determining an edge of a solartracker table. In one example, as shown in FIG. 4, ARC 204 includes fiveproximity sensors 230A-230E, however this is merely an example and anynumber of proximity sensors can be used. Due to the general dustyconditions under which solar tracker tables are used, the edge sensor orproximity sensor may be preferably embodied as an ultrasonic proximitysensor however other types of sensors, such as IR sensors, capacitancesensors and the like, can be used. As mentioned above, the proximitysensors are used with control unit 220 to prevent ARC 204 from fallingoff the side of the solar tracker table and also for allowing ARC 204 tomove accurately along the edges of the solar tracker table. Across-sectional view of ARC 204 along line A-A is shown below andexplained in FIG. 5.

FIG. 4 also shows the components of first docking station 202, includinga plurality of anchoring elements 238 and a physical barrier 244.Physical barrier 244 may be specifically positioned on the northern sideof first docking station 202 (in a northern hemisphere installation) foruse in calibrating electronic gyroscope 222 at the start of a cleaningprocess, as described below. In a southern hemisphere installation, thephysical barrier may be positioned on the southern side of the dockingstation. Plurality of anchoring elements 238 is substantially similar toplurality of anchoring elements 164 (FIG. 3). The anchoring elements areused for anchoring and recharging rechargeable power source 228 of ARC204. Each one of plurality of anchoring elements 238 includes aconductive bar 242, which can be made from a conductive metal such asstainless steel alloy 316 or other alloys, as well as a plurality ofsupporting elements 240 coupled at the ends of each conductive bar.Conductive bar 242 is used to anchor and charge the ARC on the east sideor the west side of first docking station 202. In one embodiment of thedisclosed technique, first docking station 202 may include a pluralityof anchoring elements on both the east side and the west side of thedocking station. Supporting elements 240 are flexible and with eachsupporting element 240 including a spring (not shown) for ensuringproper conductivity for recharging rechargeable power source 228. Asmentioned above ARC 204 includes a plurality of recharge connectors 232for coupling ARC 204 with conductive bar 242. Plurality of rechargeconnectors 232 are coupled with rechargeable power source 228. Also asmentioned above, first docking station 202 may include physical barrier244, which may be embodied as a vertical wall, for stopping ARC 204while it moves into first docking station 202. Physical barrier 244 canalso be used in the calibration process of at least 6-axis motion sensor246, in particular in calibrating electronic gyroscope 222.

Reference is now made to FIG. 5 which is a cross-sectional view of therobotic cleaner of FIG. 4 along a line A-A, generally referenced 260,constructed and operative in accordance with a further embodiment of thedisclosed technique. All elements and parts in FIG. are shown and havebeen explained above in FIG. 4 except for a few. Therefore identicalreference numbers are used in FIG. 5 for identical elements shown inFIG. 4. FIG. 5 additionally shows a spring 264 which supports supportingelement 240, enabling springiness and flexibility in supporting element240 and conductive bar 242. Shown additionally is an angular flatelement 262 positioned adjacent to cleaning cylinder 212 for improvingthe cleaning process by increasing the strength of the directional airflow generated by plurality of microfiber fins 214. Angular flat element262 improves the cleaning process by directing the air flow generated byplurality of microfiber fins 214 forward and thus absorbs some of thedust particles which may fly backwards while cleaning cylinder 212rotates plurality of microfiber fins 214. Angular flat element 262 makesthe directional air flow of plurality of microfiber fins 214 powerfuland strong and thereby reduces impact and pressure on theanti-reflective coating of the solar panels.

Reference is now made to FIG. 6 which is a top view of a second dockingstation, generally referenced 300, constructed and operative inaccordance with another embodiment of the disclosed technique. Similarto first docking station 202 (FIG. 4), second docking station 300 ispositioned at the northern end of a solar tracker table 152A (FIG. 3) inthe northern hemisphere (and in the southern end in the southernhemisphere). Second docking station 300 includes a docking surface 302,a plurality of supporting elements 340, a plurality of conductive bars342 and a protective wall 344. Plurality of supporting elements 340couple plurality of conductive bars 342 to docking surface 302.Plurality of supporting elements 340 can be made from any non-conductivematerial, such as polycarbonate, and are electrically isolatingelements. Each supporting element provides mechanical support andsufficient rigidity to a conductive bar and is used to position aconductive bar at the appropriate height and levelness relative todocking surface 302 such that an ARC (not shown) can recharge in thedocking station. Plurality of conductive bars 342 can be made from anyconductive material, such as a conductive alloy, stainless steel type316 and the like. Plurality of conductive bars 342 is coupled with solarpanel 162 (FIG. 3) or any other source of energy for recharging the ARC.The electrical coupling can be via a conducting wire (not shown).Plurality of conductive bars 342 are similar to conductive bars 242(FIG. 4) and are positioned at a height and distance such that rechargeconnectors 232 (FIG. 4) of an ARC can couple with then to begin arecharge process. As shown, plurality of conductive bars 342 arepositioned in an eastern side and western side of docking surface 302,as shown by the letters ‘E’ and ‘W’ in FIG. 6.

Reference is now made to FIG. 7 which is a side view of the seconddocking station of FIG. 6, along a line C-C of FIG. 6, generallyreferenced 310, constructed and operative in accordance with a furtherembodiment of the disclosed technique. Identical reference numbers toFIG. 6 are used in FIG. 7 to show the same elements as shown in FIG. 6.FIG. 7 shows that each one of plurality of supporting elements 340 iscoupled to docking surface 302 with a plurality of screws 330 and issufficiently long to be positioned at a height 346 at which each two ofplurality of supporting elements 340 is coupled with one of plurality ofconductive bars 342. Plurality of screws 330 can be embodied as any kindof fastener or rivet. Shown as well, protective wall 344 issubstantially at the same height at plurality of conductive bars 342 andis used to prevent an ARC from falling off docking surface 302 and alsoin the procedure of calibrating the electronic gyroscope of the ARC.

Reference is now made to FIG. 8 which is another side view of the seconddocking station of FIG. 6 along a line D-D of FIG. 7, generallyreferenced 320, constructed and operative in accordance with anotherembodiment of the disclosed technique. Identical elements in FIG. 8already described in FIGS. 6 and 7 are shown using identical referencenumbers. Visible in FIG. 8 is the coupling of a supporting element 340to both docking surface 302 and conductive bar 342 using plurality ofscrews 330.

With reference back to FIG. 6, an ARC (not shown) is recharged indocking station 300 in the follow manner. As docking station 300 iscoupled with solar tracker table 152A, docking station 300 tilts withsolar tracker table 152A. During the morning hours, until about noon,solar tracker table 152A faces eastward. The ARC is positioned such thatits recharge connectors face eastward as well. Due to the tilt angle ofthe solar tracker table for most of the morning hours, enough pressureis exerted by gravity on the recharge connectors of the ARC toelectrically couple then with plurality of conductive bars 342, therebyenabling the rechargeable batteries of the ARC to recharge. Around noontime, solar tracker table 152A is substantially horizontal and into theafternoon, begins to tilt in a westward direction. Once the at least6-axis motion sensor of the ARC senses that the solar tracker table hastilted sufficiently in a westward direction, control unit 220 (FIG. 4)may give a command to the ARC to make a 180° turn such that the rechargeconnectors now face the westward facing conductive bars. Again, due togravity, the ARC will exert enough pressure on the conductive bars onthe west end of docking surface 302 to couple the recharge connectorssuch that the ARC can continue recharging as the solar tracker tabletilts westwardly during the afternoon hours. The ARC may stay in thatposition until electricity production of the solar tracker tables hasceased once the sun has set. As described below, the solar trackertables are then brought to a horizontal position, at which point the ARCthen begins a cleaning cycle. In another embodiment of the disclosedtechnique, the front end of the ARC, opposite the end of rechargeconnectors 232 (FIG. 4), may also be equipped with additional rechargeconnectors (not shown) such that when solar tracker table 152A beginstilting in a westward direction, the ARC can be given a command to moveforward and couple with the conductive bars on the other side of thedocking surface and can continue its recharge cycle if needed.

As noted, since plurality of conductive bars 342 are solid and areaccurately positioned relative to docking surface 302 and solar trackertable 152A. Therefore, before a cleaning cycle begins, the ARC may usethe conductive bars on the westward side to calibrate the electronicgyroscope of the ARC to a local northern direction. Alternatively,before a cleaning cycle begins, the ARC may turn towards protective wall344, which is positioned in a northern direction, in order to calibratethe electronic gyroscope of the ARC to a local northern direction. Theconductive bars on the eastward side can also be used to calibrate theelectronic gyroscope of the ARC. It is further noted that the maindifference between first docking station 202 (FIG. 4) and second dockingstation 300 is that first docking station 202 uses springs to mountconductive bars at the height of the recharge connectors of the ARCwhereas second docking station 300 uses supporting elements which arerigid.

With reference back to FIG. 3, the ARC of the disclosed technique canalso be equipped with additional brushes, microfibers and cleaningelements for cleaning the surface of a solar tracker. In otherembodiments, the docking stations of the disclosed technique (any one ofdocking stations 160, 202 or 300) does not need to include a structurefor emptying a dust bin as the ARC may simply push dust and debris offthe surface of a solar tracker and thus the ARC is not equipped with adust container, such as shown above in ARC 204 (FIG. 4). As shown aboveand as described, ARC 204 is a waterless cleaner and clean the surfaceof a solar tracker either by pushing dirt and debris off the surface orby using air suction. According to the disclosed technique, bypositioning the solar trackers of a solar tracker park in a horizontalposition, an autonomous robot, such as those known from the vacuumcleaning industry, can be used to clean the surface of solar trackersautonomously. In a horizontal position, an autonomous robot does nothave to deal with issues of the force of gravity either in ascending aninclined solar tracker table or braking when descending such a solartracker table. As is known in the vacuum cleaning industry, variousalgorithms can be used to ensure that ARC 204 covers the entire surfaceof a solar tracker table and thus cleans the entire solar tracker table.In some embodiments of the disclosed technique, ARC 204 may furtherinclude cameras and sensors (not shown) for detecting defects on thesurface of a solar panel. ARC 204 may include at least one of a lightsource, a visible light camera, an infrared light source and an infraredcamera, for detecting defects on the surface of a solar tracker.

Docking station 160 is shown with ARC 166 in a parked position betweenplurality of anchoring elements 164. In one embodiment, in a parkedposition, ARC 166 can couple with electrical connectors (not shown) atthe edges of docking station 166 for recharging the rechargeable powersource of ARC 166. Alternatively, as shown, ARC 166 can couple withplurality of anchoring elements 164 which include conductive bars forsimultaneously recharging the rechargeable power source of ARC 166 whilealso anchoring ARC 166. As shown, bridge 158 is wide enough for ARC 166to pass onto either side of the solar tracker. According to thedisclosed technique, a plurality of ARCs is used such that each solartracker table has its own individual ARC. Each individual ARC is parkedin the docking station of a given solar tracker while not in a cleaningprocess and thus does not interrupt the electricity production of thegiven solar tracker. As shown, the docking station is external to thesolar panels of a solar tracker to avoid casting a shadow on the solarpanels of the solar tracker during daylight hours.

Since the tilt angle of the solar trackers is centrally controlled,according to the system and the method of the disclosed technique, inthe evening hours when no electricity is being produced from solarenergy, the solar trackers of the solar tracker park are brought to ahorizontal position. A horizontal position means that the east and westtilt angle is substantially zero and is substantially the position of asolar tracker at high noon. According to the disclosed technique, thehorizontal position can be anywhere between ±10° of a horizontal tiltangle (i.e., up to 10° titled in a westward direction or up to 10°tilted in an eastward direction). Once substantially horizontal, eachARC of each solar tracker is given a cleaning command to move out fromits respective docking station and to clean the horizontal surface ofthe solar tracker. As mentioned above, in one example, a zigzag path canbe used to cover and clean the entire surface of a solar tracker. Othercleaning paths, as described below, can be used as well. Each ARCincludes edge sensors or proximity sensors that prevent it from fallingoff the sides of a solar tracker. This is aided by the solar trackersbeing specifically brought to a horizontal position for cleaning, thusavoiding the additional issues and complexities of cleaning a solartracker table which is at an incline. In some embodiments, additionalphysical and/or virtual structures may be added to a solar tracker tableto prevent an ARC from falling over the edge, such as a virtual magneticwall which the ARC can detect or even the installation of a low physicalbarrier to the perimeter edge of the solar tracker. As mentioned above,most of solar trackers have two sections, so the ARC may finish cleaninga first section and then will move through bridge 158 to the othersection. As explained above, when the cleaning is done the ARC canautonomously travel back to docking station 160 over bridge 158, anchoritself safely between the anchoring elements and couple with electricalconnectors for recharging.

A control and communication system (not shown) which is part of thesolar tracker park may be used to initiate the start of the cleaningprocess of the plurality of ARCs as well as to ensure that all ARCs havereturned to their parking positions once the cleaning process hascompleted. Each ARC may additionally have a sensor ensuring that acleaning process starts only when a solar tracker is level and in ahorizontal position (or within a tilt angle of ±10 degrees). Forexample, accelerometer 224 (FIG. 4) may be used to ensure that acleaning process only begins when a solar tracker table is level. Thecontrol and communication system can also send out a stop cleaningsignal in case of inclement weather conditions such as humidity, wind orrain. The control and communication system can be embodied as a shortrange wireless network using protocols such as ZigBee or XBee. Accordingto the disclosed technique, other wireless communication protocols canbe used as well. It is noted that in the event of inclement weatherduring the cleaning process, the control and communication system maygive a command to the ARCs to return to docking station 160 and toanchor themselves to plurality of anchoring elements 164 to avoid theARCs falling off the solar tracker tables due to the bad weather. Oncethe inclement weather subsides, provided the sun has not risen yet, theARCs may be provided with a continue cleaning command to resume thecleaning cycle they had previously started. Light sensors, wind sensors,pressure sensors, humidity sensors, rain sensors and other weatherrelated sensors can be used to automatically determine if inclementweather conditions are present in the vicinity of the solar trackerpark.

With reference back to FIGS. 4 and 5, in this embodiment of the ARC,cleaning of the surface of the solar tracker tables is done by at leastone cleaning cylinder 212 equipped with a plurality of microfiber fins214. According to the disclosed technique, one or more rotationalcylinders can be used to effect the cleaning of the solar tracker tablesurface. Furthermore, plurality of microfiber fins 214 may be made fromother fabric, textile or cloth materials. In one embodiment of thedisclosed technique, the width of the microfiber fins may be 100millimeters (herein mm) and the radial size of the microfiber fins maybe between 200 to 240 mm. It is noted that other dimensions can be used.The aforementioned dimensions of the microfiber fins may ensure anoptimal generation of a directional air stream. Cleaning of the solartracker table surface is achieved by the generated directional airstream together with angular flat element 262 and also by the very softtouch and low exerted pressure of less than 0.1 g/cm² of the pluralityof microfiber fins which push dust and debris on the solar tracker tablesurface over the edge of the solar tracker table. According to thedisclosed technique, the ARC cleans a solar tracker table while thesolar tracker table is in a horizontal position but can also clean ifthe solar tracker table has a slight tilt angle of up to ±10 degreesfrom its horizontal position.

The motion and the maneuvering of the ARC on the surface of a solartracker table is controlled by control unit 220 and its processor (notshown), using left drive wheel 206A and right drive wheel 206B which aredriven by left DC drive motor 208A and right DC drive motor 208Brespectively and also using left wheel encoder 248A and right wheelencoder 248B. ARC 204 moves forwards and backwards when left drive wheel206A and right drive wheel 206B rotate in the same direction with thesame speed. ARC 204 will spin around when left drive wheel 206A andright drive wheel 206B rotate in opposite directions. Maneuvering to theright or to the left of the ARC is done by controlling the pulse widthmodulation of left DC drive motor 208A and right DC drive motor 208Bwhich can be controlled by the processor. Control unit 220 thus controlsthe cleaning process of the ARC. The number of pulses of each drivemotor can be measured using left wheel encoder 248A and right wheelencoder 248B, thereby precisely controlling the positioning of the ARC.

As mentioned above, each ARC is equipped with an at least 6-axis motionsensor, including an accelerometer and an electronic gyroscope, as wellas (for example, in the embodiment shown in FIG. 4) five proximitysensors that can sense the edges of the solar tracker table whichtogether are controlled by control unit 220. As mentioned above, each ofleft DC drive motor 208A and right DC drive motor 2088 includes at leastone encoder for counting the angular status of each drive motor whichcan be provided to control unit 220 for determining the angular positionof the rotation of each of left drive wheel 206A and right drive wheel206B.

Using all or at least some of the accelerometer, electronic gyroscope,proximity sensors and encoders, control unit 220 can navigate the ARC onthe surface of the solar tracker table in any required pattern. Inparticular, according to the disclosed technique, ARC 204 can use anaccelerometer and an electronic gyroscope for maneuvering and navigatingover the surface of a solar tracker table. As described below, theelectronic gyroscope may be calibrated using the azimuth and the localnorth of the solar tracker table before the start of a cleaning cycle.The electronic gyroscope of ARC 204 is calibrated by ARC 204 pushingagainst the protective wall which is positioned on the northern side ofthe docking station. This direction becomes the local north of theelectronic gyroscope, thereby compensating for any inaccuracies in thedirectional positioning of the solar tracker tables in a north-southdirection. Alternatively, the ARC can push against the conductive barspositioned on either the westward side or eastward side for calibratinga local direction of the electronic gyroscope. Using the local north ofthe solar tracker table as part of the calibration and navigation of theARC improves the cleaning process of the disclosed technique since theARC will move over the solar tracker in a north-south (or east-west)direction based on the actual position of the solar tracker. This isunlike the prior art, where a solar tracker may be positionednorth-south using magnetic north as the direction of positioning whereasthe prior art robotic cleaner cleaning the surface uses true north todetermine its location on the solar panel surface. It is noted as wellthat the at least 6-axis motion sensor can be substituted for a 9-axismotion sensor which includes a magnetometer as well. It is further notedthat advances in global positioning system (herein abbreviated GPS)navigation systems may yield GPS sensors having a resolution of betterthan 1 degree. When such GPS navigation systems become available, a GPSsensor may be included in the ARC of the disclosed technique, and GPSnavigation may be used as an aid to the at least 6-axis motion sensor ofthe ARC, for example for double checking and/or providing a validationcheck for the position of the ARC on the solar tracker table surface.

One cleaning pattern of the ARC may be that the ARC is moved fromdocking station 202 to the south edge of the southern section of thesolar tracker table without operating the cleaning cylinder. The ARC isthen turned westwards and starts to clean the solar tracker tablesurface in a zigzag pattern from west to east to west until the entiresurface has been cleaned. In this pattern, the cleaning is effected fromthe end to the south end of the solar tracker table. A similar patterncan be effected with the ARC going north to south to north. When the ARCreaches bridge 158 (FIG. 3), the ARC will cross the bridge while alsocleaning solar panel 162 (FIG. 3) which is used to recharge therechargeable power source of the ARC. The ARC will continue its zigzagcleaning pattern towards the north. When the ARC reaches the northernedge of the second section of the solar tracker table, the ARC will thenautonomously return to docking station 202. The ARC enters dockingstation 202 and will park facing east while recharge connectors 232press eastwards on conductive bars 242. In one embodiment, either one ofdocking stations 202 or 300 (FIG. 6) may have anchoring elements on bothits eastern and western side, such that in this embodiment, at the nexthigh noon, the ARC can turn around facing westwards and move until itsrecharge connectors press against western placed conductive bars (notshown). As mentioned above, the described pattern of cleaning andrecharging is merely an example and other cleaning patterns and rechargeprocedures are possible.

When a start cleaning command is received by the ARC, control unit 220checks the tilt position of the solar tracker table using accelerometer224. If the tilt position is horizontal (or close enough to horizontal,meaning within ±10 degrees from the horizontal), then the ARC will turnto the north and press its recharge connectors toward physical barrier244 in order to calibrate electronic gyroscope 222. The ARC thuscalibrates electronic gyroscope 222 such that its north is the localnorth of the solar tracker table. Electronic gyroscope 222 calibratesitself using the azimuth of the solar tracker table as represented bythe azimuth of physical barrier 244 and a determination of the localnorth before commencing its cleaning process. After calibration iscompleted, the ARC can turn south to start the cleaning process asdescribed above.

As part of the disclosed technique, the solar tracker park may include aweather center (not shown) including instruments and sensors such as atleast one of a wind vane and an anemometer (both not shown) fordetermining wind direction and wind speed, as well as other instrumentssuch as a thermometer, a hygrometer and the like, for determiningvarious parameters of the weather present at the solar tracker park. Incases of weather conditions such as a strong westerly wind, cleaning bythe ARC may be performed using a cleaning pattern that moves dust anddebris from west to east, thereby using the tailwind to enhance the actof cleaning. In this pattern, movements of the ARC from east to westwill be idle, without operating the cleaning cylinder. In the case of astrong easterly wind, the cleaning pattern is reversed. Thus the weathercenter can transmit data to the control unit of the ARC to clean thesolar tracker tables using specific cleaning patterns depending on thedetermined weather present at the solar tracker park.

It is noted that the disclosed technique has been described in thecontext of a solar tracker table which can tilt from east to west duringthe course of a day. However the disclosed technique can also be used onfixed angle solar tables provided their angle of tilt is not greaterthan 10° in either an eastwardly or westwardly direction. In such anembodiment, the ARC of the disclosed technique as well as the dockingstation is embodied in a similar way as described above however sincethe solar tables and panels cannot tilt, then a cleaning cycle commandis simply provided to the ARC once the sun has set, without requiring acommand to be provided to the solar tables and panels to tilt to ahorizontal tilt angle of substantially 0°.

Reference is now made to FIG. 9, which is a side view of a solartracker, positioned to enable cleaning by a robotic cleaner under strongwind conditions, generally referenced 360, constructed and operative inaccordance with a further embodiment of the disclosed technique. Similarelements between FIGS. 1 and 2 and FIG. 9 are labeled using identicalreference numbers, such as solar tracker 102, supporting pole 104 andground level 112. FIG. 9 also shows an ARC 362 which is shownschematically as having a cover (not labeled) and thus the inner partsof ARC 362 are not visible. As mentioned above, the ARC of the disclosedtechnique can clean a solar tracker table angled anywhere between −10°to +10° as measured from a horizontal tilt angle of substantially 0°. Inone embodiment of the disclosed technique, ARC 362 cleans the surface ofa solar tracker table when it is placed at a horizontal tilt angle ofsubstantially 0°. Also as mentioned above, the ARC of the disclosedtechnique is lightweight to prevent the weight of the ARC from damagingthe surface of the solar tracker tables, especially any anti-reflectivecoating which may be placed on the surface of the solar trackers. Due tothe relative lightweight of the ARC (about 10 kilograms) and its generalshape, a sufficiently strong wind may create enough lift force to liftARC 362 off the surface of solar tracker 102. Thus, certain windconditions can cause ARC 362 to flip over or to fall off the surface ofsolar tracker 102.

As shown in FIG. 9, a wind is blowing across the surface of solartracker 102, shown by a plurality of arrows 364. Based on the BeaufortScale for windstorms, supposing that wind 364 has a mean wind speed of29 kilometers per hour (herein abbreviated Km/h), wind 364 will exert awind pressure of about 4.0 kilograms per square meter (hereinabbreviated Kg/m) over the surface of solar tracker 102. Supposing thatARC 362 has an average surface area of 0.4 m², the acting wind pressureon ARC 362 due to wind 364 will be 1.6 Kg/m². The wind pressure exertedon ARC 362 can be compensated for by tilting solar tracker 102 by anangle 366 from a horizontal line 368 as measured from the pivot (notlabeled) which controls the angle of solar tracker 102. A gravity vector370 shows the downward force exerted by gravity on ARC 362 whereas anormal force vector 374 shows the normal force exerted by solar tracker102 on ARC 362. The component of gravity vector 370 which is parallel tothe surface of solar tracker 102, shown as surface vector 372, can bedetermined by the following formula:

SurfaceVector=M·g·sin α  (1)

where Surface Vector is the force of surface vector 372 in Newtons, M isthe mass of ARC 362 in kilograms and a is angle 366. Given the exampleabove, if angle 366 is about 9° then surface vector 372 should exertenough force to compensate for the wind pressure exerted by wind 364. Asmentioned above, since ARC 362 can clean the surface of solar tracker102 up to a tilt angle of around 10°, wind pressures of up toapproximately 1.7 Kg/m² can be exerted on ARC 362 which can becompensated for by the tilt angle of solar tracker 102. Such a windpressure on ARC 362 is equivalent to a mean wind speed of approximately30 Km/h according to the Beaufort Scale (the lower end of what isdescriptively referred to as a “fresh breeze” in the Beaufort Scale).Therefore, according to the disclosed technique, ARC 362 can be used toclean the surface of solar tracker 102 up to measured wind speeds ofapproximately 30 Km/h. At wind speeds higher than that, ARC 362 shouldremain in its docking station until wind speeds lessen to below 30 Km/h.

According to the disclosed technique, the master controller (not shown)which controls the tilt angle of solar tracker 102, can determine thewind pressure exerted on ARC 362 before ARC 362 leaves its dockingstation based on weather information. The weather information can beprovided by a network connection to a weather service as well as fromweather instruments (not shown) coupled with the master controller, forlocally determining the weather in the solar tracker park. The weatherinstruments may include at least one of an anemometer, a hygrometer, abarometer, a thermometer and the like for measuring and determiningvarious characteristics of the local weather. If the master controllerdetermines that a wind is present over the surface of solar tracker 102,and that the average wind speed is less than the upper limit ofapproximately 30 Km/h, then master controller can determine what titleangle solar tracker 102 should be positioned at, based on Equation 1above, such that the tilt angle compensates for the wind force. It isnoted that Equation 1 is useful for winds which generally blow in adirection in line with angle 366. As shown in FIG. 9, wind 364 blowsfrom east (E) to west (W), thus angle 366 can be used to compensate forwind pressure by a predominantly easterly or westerly wind. If the windin FIG. 9 was blowing predominantly in a northerly or southerlydirection (not shown) then the tilt of solar tracker 102 from east towest will not compensate for such wind pressures. In such a scenario,the master controller may set a lower average wind speed limit forgiving a command to ARC 362 to leave its docking station and clean thesurface of solar tracker 102. It is also noted that each solar trackertable in a solar tracker park may be equipped with weather instrumentsand that the master controller can determine a different tilt angle persolar tracker table depending on the measured average wind speed overeach solar tracker table.

Reference is now made to FIG. 10, which is a top view of a solartracker, showing a docking station as well as cleaning patterns for usein varying wind conditions, generally referenced 390, constructed andoperative in accordance with another embodiment of the disclosedtechnique. Similar elements between FIG. 3 and FIG. 10 are labeled usingidentical reference numbers, such as solar tracker table 152A, bridge158, docking station 160, solar panel 162, anchoring elements 164 andARC 166. The left side of FIG. 10 shows that docking station 160 nowincludes locking bars 392. Locking bars 392 are shown as two bars whichstretch over the length of docking station 160 and are shown in greaterdetail below in FIGS. 11 and 12. Locking bars 392 substantially create acage for ARC 166, forming an upper canopy or roof under which ARC 166can park and couple with anchoring elements 164. As shown in FIG. 10, ifstrong or even extreme easterly or westerly winds blow over solartrackers 152A and 152B, with sufficient force to lift ARC 166 off thesolar tracker surface, then when ARC 166 is parked in docking station160, the top side of the cover (not shown) of ARC 166 will come intocontact with locking bars 392, which will prevent ARC 166 from flyingoff of docking station 160. Thus according to the disclosed technique,locking bars 392 enable ARC 166 to remain in docking station 160 evenunder extreme wind conditions (with extreme being up to and includinghurricane conditions). Locking bars can be made from any tough anddurable material, such as metal, hard plastic, fiberglass and the like.

The right side of FIG. 10 shows two different cleaning patterns asexamples, according to the disclosed technique, of cleaning patternswhich can be used to increase the cleaning efficiency of ARC 166 undervarying wind conditions. As mentioned above, the master controller (notshown) of solar tracker tables 152A and 152B may be coupled with aweather service or may include weather information equipment andinstruments for determining the weather at the site of the solar trackerpark. If a wind is detected, the master controller may instruct ARC 166to clean in a particular pattern such that the direction of the wind isused to aid the cleaning of the surface of the solar tracker. In oneexample as shown, if a predominantly westerly wind, as shown by aplurality of arrows 394, is determined by the master controller, thenARC 166 may use a sweeping pattern 396 wherein ARC 166 travels in adirection perpendicular to the direction of the detected wind, advancingat each turn in a perpendicular direction in the direction of wind 394.ARC 166 thus travels from north to south and south to north over solartracker table 152B blowing dirt and debris off the solar trackersurface, and at each turn, ARC 166 advances eastward, in the directionof westerly wind 394. In this manner, ARC 166 moves dirt, debris anddust off solar tracker table 152B in the direction of wind 394. ARC 166thus moves dirt, debris and dust forward onto as yet uncleaned areas ofthe solar tracker table surface, in the same general direction whichwind 394 is blowing dirt, debris and dust over solar tracker table 152B.The force of wind 394 can therefore be used along with the directionalair stream (not shown) of ARC 166 to increase the cleaning efficiency ofARC 166. As another example, if a predominantly southerly wind, as shownby a plurality of arrows 398, is determined by the master controller,then ARC 166 may use a sweeping pattern 400 wherein ARC 166 travels in adirection perpendicular to the direction of the detected wind, advancingat each turn in a perpendicular direction in the direction of wind 398.ARC 166 thus travels from east to west and west to east over solartracker table 152A blowing dirt and debris off the solar trackersurface, and at each turn, ARC 166 advances northward, in the directionof southerly wind 398. Similar cleaning patterns are possible accordingto the disclosed technique for northerly and easterly winds (both notshown). According to the disclosed technique, before a command is givento ARC 166 to clean the surface of solar tracker tables 152A and 152B,the master controller determines if a strong enough wind is present,blowing predominantly in one of the cardinal directions. If so, mastercontroller can give ARC 166 a specific command to clean in a sweepingpattern as shown in FIG. 10, wherein the direction of the determinedwind is used to increase the efficiency of the cleaning of dirt anddebris off the surface of the solar tracker tables by ARC 166. Accordingto another embodiment of the disclosed technique, ARC 166 can be given acommand to clean a solar tracker table surface using a sweeping patternregardless of the direction of the determined wind. In this embodiment,ARC 166 can clean by pushing dirt and debris off the solar tracker tablesurface following a sweeping pattern wherein ARC 166 travels over thesolar tracker surface in a direction perpendicular to the direction ofthe determined wind and at each turn, advancing in the direction of thewind. Thus the sweeping patterns shown in FIG. 10 can be embodied forany wind direction and are not limited to winds only blowingpredominantly in the four cardinal directions.

Reference is now made to FIG. 11, which is a magnified top view of thedocking station of FIG. 10, generally referenced 410, constructed andoperative in accordance with a further embodiment of the disclosedtechnique. Shown in FIG. 11 is a portion 412 of a solar tracker table, adocking station 414, substantially similar to docking station 160 (FIGS.3 and 10), an ARC 416 and a plurality of anchoring and charging elements418. ARC 416 is shown in outline as a dotted line to delineate itsposition in docking station 414. Docking station 414 includes lockingbars 420, an end wall 424 and at least two entrance walls 422. End wall424 and entrance walls 422 are the height of ARC 416, with end wallstretching the length of docking station 414 and entrance walls 422being spaced apart enough for ARC 416 to enter and exit. End wall 424and entrance walls 422 act as physical barriers to prevent ARC 416 fromflying off of docking station 414. Entrance walls 422 can also beembodied as a single entrance wall (not shown), longer in length thaneither one of entrance walls 422 as shown in FIG. 11 and serving thesame function as a physical barrier to prevent ARC 416 from flying offof docking station 414. Locking bars 420, as shown, extend the length ofdocking station 414 and are permanently attached to docking station 414,forming a partial canopy or roof protection under which ARC 416 coupleswith plurality of anchoring and charging elements 418 when ARC 416returns to docking station 414 to recharge and/or during inclementweather. Locking bars 420, end wall 424 and entrance walls 422 togetherform a protective barrier for protecting ARC 416 from lifting off ofdocking to station 414 during extreme wind conditions, thus protectingARC 416 even during hurricane level winds. As explained above, lockingbars 420 are spaced over docking station 414 such that if a strongenough wind, either from an easterly or westerly direction, exerts alift force on ARC 416, the top of ARC 416 will be stopped by lockingbars 420, which prevent ARC 416 from flying off of docking station 414.If a strong southerly wind pushes against ARC 416 in the direction ofnorth, with enough strength to move ARC 416 such that its wheels arepushed in a perpendicular direction, then end wall 424, being at theheight of ARC 416, will prevent ARC 416 from falling off the northernside of docking station 414. Likewise, if a strong northerly wind pushesagainst ARC 416 in the direction of south, with enough strength to moveARC 416 such that its wheels are pushed in a perpendicular direction,then entrance walls 422, being at the height of ARC 416, will preventARC 416 from moving sideways off of docking station 414 and possibly offof solar tracker table 412.

Reference is now made to FIG. 12, which is a side view of the dockingstation of FIG. 10, generally referenced 440, constructed and operativein accordance with another embodiment of the disclosed technique.Similar elements between FIG. 5 and FIG. 12 are labeled using identicalreference numbers, such as solar tracker table 202, cleaning cylinder212 and plurality of microfiber fins 214. Shown in FIG. 12 is a cover442, covering the inner components of ARC 204 as well as a locking bar446. As shown, one end of locking bar 446 is coupled with an end ofdocking station 202, as shown by an arrow 448. Locking bar 446 ispermanently fixed to docking station 202 and thus acts as a type of cagefor preventing ARC 204 from lifting off docking station 202 undersufficient wind conditions. As shown by an arrow 450, sufficient windconditions can cause ARC 204 to lift in the direction of arrow 450.However if that begins to happen, the presence of locking bar 446prevents ARC 204 from fully lifting off of docking station 202.

As mentioned above, the disclosed technique also provides for a methodand system for improved weather information sharing during operation andcleaning of a solar tracker park and for improving predicted maintenanceand machine learning of maintenance of the solar tracker park. Accordingto the disclosed technique, a solar tracker park or farm may include amaster controller for each solar tracker table as well as a mastercontroller for the entire solar tracker park. Each master controller maybe coupled with every other master controller and/or with the mastercontroller of the entire solar tracker park such that information can beexchanged between these components. The information can include weatherinformation as well as information about the current status of eachsolar tracker table. As explained above, the exchange of weatherinformation between the various master controllers is used for optimaland safe operation of the ARCs in the solar tracker farm. It is notedthat this exchange of information can be expanded to other aspects ofthe operation of a solar tracker park, such as the tilt accuracy of eachsolar tracker table, any breakage in the solar panels of a solar trackertable, cracks and microcracks on the solar panel surface of a solartracker table, and the like.

This exchange of information can be entered as part of a predictivemaintenance algorithm for determining when different types ofmaintenance should be performed on the solar trackers of the solartracker park. This exchange of information can also be used for solartracker park maintenance and management. According to one embodiment ofthe disclosed technique, each solar tracker table may include at leastone weather related instrument, such as an anemometer, thermometer,hygrometer, barometer and the like, such that the specific weatherconditions of a given solar tracker table can be determined. Suchweather information can be used to give individuals ARCs differentcleaning instructions as well as angling individual solar trackers atdifferent cleaning angles depending on the wind conditions determined atdifferent parts of the solar tracker farm. For example, if a strongeasterly wind is present, it may be that solar trackers on the easternside of the solar tracker park will be given instructions to have theirARCs stay under the shelter of the locking bars of the docking stationswhereas ARCs on the western side of the solar tracker park, where theremay be less wind, will be given instructions to clean their respectivesolar tracker tables with the solar tracker tables positioned at aspecific cleaning angle. In addition, in such a scenario, on the westernside of the solar tracker park, different solar trackers may bepositioned at different cleaning angles depending on the measured windforce on each solar tracker table.

It will be appreciated by persons skilled in the art that the disclosedtechnique is not limited to what has been particularly shown anddescribed hereinabove. Rather the scope of the disclosed technique isdefined only by the claims, which follow.

1. A solar tracker waterless cleaning system for cleaning solar panelsof a solar tracker, said solar tracker being able to be positioned at apre-determined angle, said solar tracker waterless cleaning systemcomprising: a docking station, coupled with an edge of said solartracker; and an autonomous robotic cleaner (ARC), said ARC comprising:at least one rechargeable power source; at least one cleaning cylinder,for cleaning dirt off of a surface of said solar tracker without water;and a controller, for controlling a cleaning process of said ARC and fortransmitting and receiving signals to and from said ARC, said controllercomprising a motion sensor, for determining an angle of said solartracker and a heading of said ARC; said at least one cleaning cylinderfurther comprising a plurality of fins which rotates for generating adirectional air flow for pushing said dirt off of said surface of saidsolar tracker; said docking station comprising at least one electricalconnector for recharging said rechargeable power source, wherein saidARC can anchor in said docking station; wherein said ARC cleans saidsolar tracker when said solar tracker is positioned at saidpre-determined angle; wherein said pre-determined angle is between −10to +10 degrees from a horizontal angle of zero degrees; wherein saidmotion sensor is used for navigating said ARC over said surface of saidsolar tracker; wherein said plurality of fins touches said surface ofsaid solar tracker when said plurality of fins rotates; and wherein saidARC cleans said solar tracker by said directional air flow and saidtouch of said plurality of fins pushing said dirt off of said surface ofsaid solar tracker while said motion sensor navigates said ARCautonomously over said surface of said solar tracker.
 2. The solartracker waterless cleaning system according to claim 1, said solartracker comprising: a first section of solar panels; a second section ofsolar panels; a bridge, for coupling said first section to said secondsection; and a recharging section of solar panels.
 3. The solar trackerwaterless cleaning system according to claim 2, said docking stationfurther comprising a conductive wire, for coupling said at least oneelectrical connector with said recharging section of solar panels,wherein electricity generated by said recharging section of solar panelsis used for recharging said rechargeable power source.
 4. The solartracker waterless cleaning system according to claim 1, wherein saidmotion sensor comprises at least one sensor selected from the listconsisting of: an accelerometer; an electronic gyroscope; and amagnetometer.
 5. The solar tracker waterless cleaning system accordingto claim 1, said docking station further comprising a plurality ofanchoring elements, each one of said plurality of anchoring elementscomprising: a plurality of supporting elements; at least one conductivebar, coupled between at least two of said plurality of supportingelements; and a physical barrier, positioned on a north side of saiddocking station, for preventing said ARC from falling from said dockingstation, wherein said at least one conductive bar is said at least oneelectrical connector, wherein said at least one conductive bar alsoanchors said ARC; wherein said plurality of supporting elements arerigidly coupled with a docking surface of said docking station; andwherein at least one of said physical barrier and said at least oneconductive bar is used for calibrating said motion sensor to a localnorth of said solar tracker.
 6. The solar tracker waterless cleaningsystem according to claim 1, said ARC further comprising: at least twodrive wheels; at least two respective direct current (DC) drive motors,for respectively driving each of said at least two drive wheels; atleast two respective drive belts, for coupling each of said at least twodrive wheels to said at least two respective DC drive motors; a supportstructure, for supporting a rear section of said ARC; at least one edgesensor, for determining an edge of said solar tracker and at least tworecharge connectors, coupled with said rechargeable power source, forelectrically coupling said rechargeable power source with said at leastone electrical connector of said docking station, wherein each one ofsaid at least two drive wheels comprises at least one respectiveencoder.
 7. The solar tracker waterless cleaning system according toclaim 1, said ARC further comprising: at least one cleaning cylinderdirect current (DC) drive motor, for driving said at least one cleaningcylinder; a cleaning cylinder drive belt, for coupling said at least onecleaning cylinder DC drive motor with said at least one cleaningcylinder; and an angular flat element, wherein said angular flat elementdirects said directional air flow generated by said plurality of finsforward.
 8. The solar tracker waterless cleaning system according toclaim 1, wherein said plurality of fins is fabricated from a materialselected from the list consisting of: microfiber; fabric; textile; andcloth materials.
 9. The solar tracker waterless cleaning systemaccording to claim 1, wherein said rechargeable power source is arechargeable battery selected from the list consisting of: a Ni-MHbattery; a lead acid battery; a lithium ion battery; a LiFePO4 battery;and a NiCad battery.
 10. The solar tracker waterless cleaning systemaccording to claim 1, said controller further comprising: a processor;and a transmitter-receiver.
 11. The solar tracker waterless cleaningsystem according to claim 1, wherein said pre-determined angle issubstantially zero degrees from said horizontal angle.
 12. The solartracker waterless cleaning system according to claim 6, wherein said atleast one edge sensor is selected from the list consisting of: aproximity sensor; an ultrasonic proximity sensor; an IR sensor; and acapacitance sensor.
 13. The solar tracker waterless cleaning systemaccording to claim 1, wherein said ARC pushes said dirt off of saidsurface of said solar tracker using a pre-defined path.
 14. The solartracker waterless cleaning system according to claim 13, wherein saidpre-defined path is selected from the list consisting of: a zigzag path;a scanning path; and a sweeping path.
 15. The solar tracker waterlesscleaning system according to claim 1, wherein said motion sensor iscalibrated to a local north along a physical barrier in said dockingstation before a start of said cleaning process.
 16. The solar trackerwaterless cleaning system according to claim 1, wherein said directionalair flow minimizes a pressure exerted on an anti-reflective coatingcovering said solar panels.
 17. The solar tracker waterless cleaningsystem according to claim 1, for cleaning said solar panels of saidsolar tracker under varying wind conditions, said solar trackerwaterless cleaning system further comprising a master controller, forreceiving and transmitting data to and from said solar tracker and saidARC, said docking station further comprising a plurality of lockingbars, coupled with said docking station, for protecting said ARC duringsaid varying wind conditions, wherein said master controller determinesan average wind speed and provides a clean command to said ARC if saidaverage wind speed is below a predetermined threshold.
 18. The solartracker waterless cleaning system according to claim 17, said dockingstation further comprising: a plurality of anchoring elements, each oneof said plurality of anchoring elements comprising: a plurality ofsupporting elements; and at least one conductive bar, coupled between atleast two of said plurality of supporting elements; and at least twophysical barriers, a first one of said at least two physical barrierspositioned on a north side of said docking station and a second one ofsaid at least two physical barriers positioned on a south side of saiddocking station, for preventing said ARC from falling off of saiddocking station, wherein said at least one conductive bar is said atleast one electrical connector; wherein said at least one conductive baralso anchors said ARC; and wherein said plurality of supporting elementsare rigidly coupled with a docking surface of said docking station. 19.The solar tracker waterless cleaning system according to claim 17,wherein said plurality of locking bars is made from a material selectedfrom the list consisting of: metal; hard plastic; and fiberglass. 20.The solar tracker waterless cleaning system according to claim 17,wherein said master controller is coupled with a weather informationcenter via a network.
 21. The solar tracker waterless cleaning systemaccording to claim 17, wherein said master controller is coupled with atleast one weather instrument for locally determining the weather at alocation of said solar tracker.
 22. The solar tracker waterless cleaningsystem according to claim 21, wherein said at least one weatherinstrument is selected from the list consisting of: a thermometer; ahygrometer; a barometer; and an anemometer.
 23. The solar trackerwaterless cleaning system according to claim 17, wherein said mastercontroller further determines a wind direction and wherein said mastercontroller provides a command to said solar tracker to position itselfat a tilt angle according to said determined average wind speed and saiddetermined wind direction, said tilt angle compensating for a wind forceof said determined average wind speed and said determined winddirection.
 24. The solar tracker waterless cleaning system according toclaim 17, wherein said master controller further determines a winddirection, and wherein said master controller provides a command to saidARC to clean said solar panels in a sweeping pattern perpendicular tosaid determined wind direction and advancing in said determined winddirection.
 25. The solar tracker waterless cleaning system according toclaim 17, wherein said master controller receives weather informationand aggregates said weather information along with said data to improvepredictive maintenance of said solar tracker.
 26. The solar trackerwaterless cleaning system according to claim 17, wherein saidaggregation enables machine learning of a maintenance cycle of saidsolar tracker.
 27. Method for waterlessly cleaning a solar trackercomprising at least one autonomous robotic cleaner (ARC) which cleanswithout water, said ARC comprising a motion sensor for navigation, saidsolar tracker being able to be positioned at a pre-determined angle,comprising the procedures of: positioning said solar tracker at saidpre-determined angle during nighttime hours, wherein said pre-determinedangle is between −10 to +10 degrees from a horizontal angle of zerodegrees; calibrating said motion sensor to a local north relative tosaid solar tracker; providing a start clean signal to said ARC to cleana surface of said solar tracker; and cleaning said solar tracker byusing a directional air flow to push dirt off of said surface of saidsolar tracker, wherein said ARC navigates autonomously over said surfaceof said solar tracker using said motion sensor.
 28. The method forwaterlessly cleaning according to claim 27, wherein said pre-determinedangle is substantially zero degrees from said horizontal angle.
 29. Themethod for waterlessly cleaning according to claim 27, said solartracker further comprising a docking station with a plurality ofanchoring elements, further comprising the procedure of providing areturn to docking station signal to said ARC when inclement weather isdetected.
 30. The method for waterlessly cleaning according to claim 27,wherein said procedure of cleaning said solar tracker comprises thesub-procedure of pushing said dirt off of said surface of said solartracker using a pre-defined path.
 31. The method for waterlesslycleaning according to claim 30, wherein said pre-defined path isselected from the list consisting of: a zigzag path; a scanning path;and a sweeping path.
 32. The method for waterlessly cleaning accordingto claim 27, wherein said procedure of cleaning said solar tracker usingsaid directional air flow minimizes a pressure exerted on ananti-reflective coating covering solar panels of said solar tracker. 33.The method for waterlessly cleaning according to claim 27, said solartracker being under varying wind conditions, further comprising theprocedure of determining an average wind speed and wind direction oversaid solar tracker before said procedure of calibrating, wherein saidprocedure of providing said start clean signal comprises thesub-procedure of providing said start clean signal to said ARC if saiddetermined average wind speed is below a pre-determined wind threshold;and wherein said ARC cleans said surface using a sweeping patternperpendicular to said determined wind direction and advancing in saiddetermined wind direction.
 34. The method for waterlessly cleaningaccording to claim 33, further comprising the procedures of: determininga solar tracker tilt angle for compensating for a wind force of saiddetermined average wind speed and said determined wind direction; andpositioning said solar tracker at said compensating tilt angle beforesaid sub-procedure of providing said start clean signal.
 35. The methodfor waterlessly cleaning according to claim 33, further comprising theprocedures of: aggregating weather information at a location of saidsolar tracker with data related to an operation of said ARC to improvepredictive maintenance of said solar tracker; and aggregating saidweather information and said data for enabling machine learning of amaintenance cycle of said solar tracker.
 36. A fixed angle solar tablewaterless cleaning system for cleaning solar panels of a solar table,said solar table being fixed at a pre-determined angle, said solar tablewaterless cleaning system comprising: a docking station, coupled with anedge of said solar table; and an autonomous robotic cleaner (ARC), saidARC comprising: at least one rechargeable power source; at least onecleaning cylinder, for cleaning dirt off of a surface of said solartable without water; and a controller, for controlling a cleaningprocess of said ARC and for transmitting and receiving signals to andfrom said ARC, said controller comprising a motion sensor, fordetermining a heading of said ARC; said at least one cleaning cylinderfurther comprising a plurality of fins which rotates for generating adirectional air flow for pushing said dirt off of said surface of saidsolar table; said docking station comprising at least one electricalconnector for recharging said rechargeable power source, wherein saidARC can anchor in said docking station; wherein said pre-determinedangle is between −10 to +10 degrees from a horizontal angle of zerodegrees; wherein said motion sensor is used for navigating said ARCautonomously over said surface of said solar table; wherein saidplurality of fins touches said surface of said solar table when saidplurality of fins rotates; and wherein said ARC cleans said solar tableby said directional air flow and said touch of said plurality of finspushing said dirt off of said surface of said solar table.
 37. The solartracker waterless cleaning system according to claim 1, wherein in saiddocking station, said at least one rechargeable power source remainscoupled with said at least one electrical connector while said solartracker changes angles.